Fluid operated stepping motor

ABSTRACT

A fluid operated stepping motor has a rotor with a plurality of ramps. A plurality of pistons are positioned in the stator of the motor on opposite sides of the rotor in alignment with the rotor axis to rotate the rotor. A logic circuit is adapted to accept a digital signal to rotate the rotor a discrete amount in either a clockwise or counterclockwise direction. The logic circuit actuates only certain pistons which stroke to rotate the rotor. The position of the rotor determines which of the pistons will be stroked upon receipt of the next signal by the logic circuit.

O Unlted States Patent 1 1 3,66 1,059 Hunter et al. 45 M 9, 1972 54]FLUID OPERATED STEPPING MOTOR 3,075,504 1/1963 Vogel ..91/491 1,939,88712/1933 Ferris et a1 ...91/193 [72] Invenms' f Gmbyi Ray'mnd 1,622,9863/1927 Weingartner ..91/5o2 Thompson, Simsbury, both of Conn.

[73] Assignee: Chandler Evans Inc., West Hartford, FOREIGN PATENTS ORAPPLICATIONS Conn- 542,789 5/1922 France ..91/502 [22] Filed: Feb 191970 592,271 1/1934 Germany ..9l/499 [21] Appl. No.2 12,585 PrimaryExaminer-William L. Freeh At10rneyRadford W. Luther [52] US. Cl..9l/499, 91/192, 99110119934, [57] ABSTRACT 51 1 Int. Cl ..F0ll 15/00,FOlb 3/00 A fluid operated pp g motor has a rotor h a p u ty of [58]Field of Search ..91 40, 183, 170, 189, 192, P A plurality of Pistonsare Positioned in the Stator of the 91/193, 194, 498, 499, 502, 476motor on opposite sides of the rotor in alignment with the rotor axis torotate the rotor. A logic circuit is adapted to ac- [561 ReferencesCited cept a digital signal to rotate the rotor a discrete amount ineither a clockwise or counterclockwise direction. The logic UNITEDSTATES PATENTS circuit actuates only certain pistons which stroke torotate the rotor. The position of the rotor determines which of the3,424,059 H1969 Conner El al. pistons be Stroked p ip f the next ig h3,237,641 3/1966 Audemar ..91/40 logic Circuit 2,882,831 4/1959Dannevig... ....9l/498 1 ,948,5 26 2/1934 Liles ..9 1/1 93 11 Claims, 6Drawing Figures Zip Zia

Zia-

PATENTEDHAY 9 1972 SHEET 2 BF 5 W 5 W V 0 WW Mum Z F PATENTEDMAY 919723,661,059

sum 5 0F 5 FIC3-6 BACKGROUND OF THE INVENTION The invention relatesgenerally to stepping motors and more particularly to fluid operatedstepping motors.

The majority of commercially available stepping motors are of theelectrical permanent magnet or variable reluctance type. Although thesemotors are capable of high stepping rates and fine resolution, theiroutput power capability is limited. Since the power available from astepping motor is largely determinative of its performance with respectto starting and stopping loads without unacceptable error a large outputpower capability is often desirable.

One of the most prominent limitations that confronts systems designersis the decrease in torque with increasing speed. Obviously, suitablegearing will provide torque gains, but this, of course, will result inreduced speed. Therefore, for applications such as numericallycontrolled machine tools and automatic welding equipment, utilization ofan electrical stepping motor usually necessitates some form of power ortorque amplification, thereby increasing the complexity of the steppingmotor. It should be noted, however, that hydraulic amplification isinvariably the form selected because it promotes high stiffness and fastresponse and is convenient with respect to flexibility of design.

Various schemes have been devised to decrease the torque requirements ofthe motor and thus overcome the problem mentioned above. One of thesemethods involves permitting the motor to accelerate over the first fewsteps and decelerate over the last few steps. This method, however, isbasically limited to pre-programmed operations wherein the stop pointcan be accurately anticipated.

Also, many prior art stepping motors do not unite high torque,bi-directional operation and positive locking capabilities. Thesefeatures are particularly desirable in applications such as controlsurface actuation and leading edge controls on high performanceaircraft.

SUMMARY OF THE INVENTION The invention provides a stepping motor with alogic system which accepts a digital signal to accurately position therotor of the stepping motor. The rotor of the stepping motor ispositioned by a plurality of actuating piston assemblies which generatea torque on the rotor and further provide positive step locking. Onlycertain pistons stroke in response to each digital signal, and the otherpistons subsequently stroke in response to succeeding signals. The rotorof the invention comprises a plurality of ramps on both sides thereof,on which output members of the piston assemblies are adapted to slide,and thereby rotate the rotor by force transfer.

A stepping motor according to the invention is advantageous in that itis capable of producing a high output torque and is operable in abi-directional manner after completion of any step. Further, thisstepping motor concept facilitates integral packaging and permits adesign with a minimum number of external connections.

A primary object of the invention is to provide a stepping motor capableof delivering a high output torque in a bidirectional manner.

Another object is to provide a stepping motor which features a positivelock in the discrete positions thereof.

A further object is to provide a stepping motor in which the outputmember thereof is capable of being accurately and discretely positioned.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description when consideredin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partlyin section, of an output device according to the invention.

FIG. 2 is a front elevational view, partly in section, of the device ofFIG. 1.

FIG. 3 is a schematic view of a hydropneumatic control circuit for thedevice of FIG. 1.

FIG. 4 is a partial schematic view of a hydroelectric control circuitfor the device of FIG. 1.

FIG. 5 is a schematic view of a hydraulic locking circuit for thehydroelectric control circuit of FIG. 4.

FIG. 6 is a schematic view of a power valve of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Turning now to thedrawings, wherein like numerals are used throughout to designate likeelements, FIGS. 1 and 2 show an output device, generally indicated atI0, of a stepping motor according to the invention. Output device 8comprises a rotor 10 having a cyclic edge profile on both sides thereoffixedly mounted upon an output member 12. Rotor 10 has a plurality oframps 14 and 16 machined on each side thereof. The ramps respectivelyconverge along lines 18 so as to divide the rotor into an equal numberof parts. On the sides of the rotor, planar surfaces 20 are machinedbetween ramps 14 and 16. Each ramp and surface occupies an angleapproximately equal to the desired step size. The angle occupied by eachsurface 20 is slightly less than the step size and the angle occupied byeach ramp is slightly greater than the step size for reasons explainedhereinafter.

As best shown in FIG. 3, rotor 10 is driven by a plurality of actuators22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, and 33, wherein only threeof the actuators 22, 23, and 24 are shown. The actuators 22-33respectively include cylinders 22c, 23c, 240, etc., pistons 22p, 23p,24p, etc., slideably mounted therein, and pointed output rods 22s, 23s,24s, etc., which are securely attached to the pistons and are arrangedparallel to axis of the rotor. Three of the actuators 22, 23, and 24 aremaster actuators and have sequencing ports 22a, 23a, and 24a in therespective cylinders thereof which function as a discrete feedbackcontrol for the logic circuit as is explained hereinafter. At the closedor left ends of the cylinders, respective pressure lines 22e, 23e, 24e,etc. are connected to communicate with the respective chambers 22b, 23b,24b, etc., defined between the cylinders and pistons. These lines areadapted to transmit the fluid which actuates the pistons. It will benoted from FIG. 3, that three groups of actuators, designated I, II andIII, control the rotation of the rotor 10, each group including onemaster actuator. All of the actuators of a particular group stroke inunison when pressure is directed thereto. It can be observed from FIGS.1 and 2 that two actuators of group I are spaced at 180 intervals on oneside of the rotor while the other two actuators of group I are similarlyspaced at 180 intervals on the other side of the rotor and lie inrespective axial alignment with the first two actuators. Each actuatoris orientated in the stator such that it is parallel to axis of therotor. Therefore, the actuators of group I are generally disposed in acommon plane. The actuator group arrangement ensures axial balance ofthe rotor during actuation. The actuators of groups II and III arearranged in a similar fashion, but respectively lie in planes spaced 60and from the plane of the group I actuators.

In FIG. 3 a logic circuit generally designated at 36 is adapted toselectively control the actuators by directing high or low hydraulicpressure to the actuator groups in accordance with a pneumatic digitalinput signal and feedback signals from the sequencing ports. The logiccircuit comprises six identical pilot valves 38, 40, 42, 44, 46 and 48,and three identical power valves 50, 52 and 54. Two pilot valves (aclockwise valve and a counterclockwise valve) and one power valve areassociated with each actuator group.

Each pilot valve has a housing 56 having a signal port 58, an inletpressure port 60, an outlet port 62, and a vent port 64. An enclosure 66is secured to the housing 56 so as to define an outlet pressure chamber67a which communicates with outlet port 62, and an inlet pressurechamber 67b which communicates with inlet port 60. Enclosure 66 hascircular openings 68 and 70 respectively formed in the top and bottomwalls thereof. Annular valve seats 72 and 74 respectively surroundopenings 68 and 70. A dividing wall 76, having an opening passingtherethrough, extends across the lower portion of the housing and isfixedly secured thereto. A diaphragm 78 is sealingly attached to thehousing 56 below wall 76 to thereby define a signal chamber 80 and avent chamber 82 which respectively communicate with signal port 58 andvent port 64. A compression spring 84 is interposed between wall 76 anddiaphragm 78 to spring bias the diaphragm in a downward sense. A spool86, having spaced lands 88 and 90 thereon, is securely fastened todiaphragm 78 and axially extends through openings 68 and 70 and theopening in wall 76. In the absence of a pneumatic pressure signal toport 58, spool 86 occupies the illustrated position in which the lands88 and 90 are spring biased to engaging positions with respective seats72 and 74, thereby preventing fluid communication between chambers 67band 67a.

When a pneumatic signal is delivered to signal port 58, a pressure riseoccurs in chamber 80 which results in upward movement of diaphragm 78.This upward motion is transmitted to spool 86 and thus to the lands 88and 90, thereby causing them to unseat and establishing communicationbetween chambers 67a and 67b. Conversely, cessation of this signalresults in downward movement of diaphragm 78 because of the influence ofthe spring force and area imbalance, thereby causing the lands to seatand discontinuing fluid communication between chambers 67a and 67b.

Power valves 50, 52 and 54 each comprise a housing 92 which includes asupply port 94, signal port 96, vent port 98, pressure outlet port 100,actuator control port 102, and drain port 103. Housing 92 also includesannular abutments 104 and 106 which serve as valve seats. Two spaceddiaphragms 108 and 110 are sealingly affixed to the sides of housing 92to define a vent chamber 112 therebetween which lies in communicationwith vent port 98. A spool 114 extends through the central portion ofdiaphragm 110 and is sealingly secured thereto. The upper extremity ofspool 114 is attached to diaphragm 108. A land 116 formed on the lowerportion of spool 114 is adapted to move between an upper position inwhich it seals off the passage formed by annular abutment 104, and alower position in which it seals off the passage formed by annularabutment 106.

In response to an appropriate hydraulic pressure signal at port 96, land116 is driven downwardly from the illustrated position in power valve 50to a position which corresponds with the illustrated position of powervalve 52. It will be noted that when land 116 is in the position shownin power valve 52, actuator control port 102 communicates with supplyport 94 via the passage defined by annular abutment 104, while in theposition shown in power valve 50, actuator control port 102 communicateswith drain port 103. Pressure outlet port 100 is in communication withsupply port 94 irrespective of land 116s position. The diaphragms usedin the pilot and power valves contribute to fast response, compactdesign, dirt insensitivity and low leakage.

Before engaging in a detailed discussion of the logic circuit it wouldbe profitable to note the various pressures to which the system of FIG.3 is exposed. Clockwise signal conduit 120 and counterclockwise signalconduit 122, which fluidly communicate with chambers 80 in the clockwiseand counterclockwise pilot valves, are in communication with a source ofpneumatic pressure during application of respective clockwise andcounterclockwise control signals. Supply ports 94 of the power valvesare in constant communication with a source of hydraulic supply pressurevia supply conduit 124. Drain ports 103 of the power valves are inconstant communication with a source of hydraulic drain pressure (tankpressure). The sides of the rotor and the mouth of each cylinder (22c330) are also exposed to static hydraulic drain pressure.

The conduits, which interconnect the pilot valves and power valves withthe master actuators 22 24, are arranged so that the actuators receivehydraulic pulses which comport with stepped motion of rotor 10. Twobranch conduits 126 and 128 are respectively connected to pressureoutlet port and actuator control port 102 and joined to pressure line22a at 130. Similarly, branch conduits 132, 134 and 136, 138 arerespectively connected to the corresponding ports in power valves 52 and54. Branch conduits 132, 134 and 136, 138 join with the respectivepressure lines 23c and 24e at junctures 140 and 142 respectively. Ducts144, 146 and 148 communicate with respective lines 22, 23a and 24e totransmit pressures therein to the other actuators of each group.

Unequally sized orifices 150 and 152 are respectively mounted within thebranch conduits 126 and 132 to provide a bias torque on the rotor. Theorifices 150 and 152 perform an ancillary function in that they merelyassure the subsequent proper ositioning of the actuators in the eventthat supply pressure is depleted, through design or inadvertence, andany of the following occur alone or in concert:

A. The column of fluid which holds the power valve in the open positionleaks away through the seats in the pilot associated valves, therebycausing the power valve to return to the closed osition;

B. The rotor is displaced to an arbitrary position by an external force.The inclusion of the orifices of different sizes resolves theseundesirable contingencies by providing a bias torque upon return of thesupply pressure which drives the actuators into a sequencingconfiguration, as exemplified by FIG. 3.

To illustrate this particular design feature assume, for example, thatorifice 150 is smaller than orifice 152 and that the power valves alloccupy closed positions. When the supply pressure returns, chamber 24bwill receive the highest pressure and chamber 22b will receive thelowest pressure, while chamber 23b will receive an intermediatepressure. Therefore, the group of actuators which is associated with thehigher pressure and whose shafts abut a ramp will supply the bias torqueafter the supply pressure is reestablished.

Sequencing conduits 154, 156 and 158 are respectively connected to thecylinders 22c, 23c and 240 at ports 22a, 23a and 24a to transmitfeedback signals, representative of discrete rotor positions, to thelogic circuit. These sequencing conduits respectively bifurcate intosegments (154a, 1541;), (156a, 1561;) and (1580, 1581;). The segments154a, 156a and 158a are in respective communication with the inletpressure ports 60 of the clockwise pilot valves 40, 42 and 38 and thesegments 1541;, 156b and 15811 are in respective communication with theinlet pressure ports60 of the counterclockwise pilot valves 48, 44 and46. It will be noted from FIG. 3 that sequencing conduits 154, 156 and158 communicate with static drain pressure when the respective shafts oftheir associated actuators are adjacent the surfaces 20 and with supplypressure behind the pistons when the respective shafts abut lines 18 onrotor 10. Thus, in the illustrated configuration of FIG. 3, the inletpressure ports 60 (and hence chambers 67b) of pilot valves 38, 40, 46and 48 are in communication with drain pressure, while the inletpressure ports of pilot valves 42 and 44 are in communication withsupply pressure.

Power valve signal pressure conduits 160, 162 and 164 fiburcate intosegments (a, 1601;), (Zea, 16212) and 164a, 1641;) to fluidlyinterconnect the outlet ports of the pilot valves with the signal ports96 of the power valves. FIG. 3 reveals that outlet ports 62 of pilotvalves (38, 44), (40, 46), and (42, 48) respectively communicate withthe signal ports 96 of power valves 50, 52 and 54, thereby transmittingthe pressure in chambers 67a to the associated signal ports. If a signalport is in communication with a high supply pressure in chamber 67a, itsassociated spool is disposed in the position shown for power valve 52.Conversely, if a signal port is in communication with a low (drain)pressure in chamber 67a its associated spool is in the position shown ineither power valve 50 or 54.

As previously set forth, each surface 20 occupies an angle which is lessthan that occupied by each ramp. The amount by which the angle occupiedby each ramp exceeds the step size is equal to half of the amount bywhich step size exceeds the angle occupied by each surface. Theunderlying reason for this rotor geometry is that it is desirable tohave the actuator rods overlie the ramps prior to the commencement of apower stroke to insure that the pointed ends of the rods do not bind onthe intersections of the surfaces and the ramps at the inception of thestroke.

Assuming that it is desired to move the rotor 10 through one step in aclockwise manner and that the configuration of the output device 8 ofFIG. 1 is as shown in FIG. 3, it is necessary to direct a pneumaticdigital pulse of specific magnitude and duration to clockwise signalconduit 120. As explained heretofore, the application of such a pulseresults in communication between chambers 67a and 67b by virtue of theunseating of lands 88 and 90 of the clockwise pilot valves. It isimportant to stress that all of the clockwise pilot valves operate inunison during application of a pulse, as is, of course, also the casewith the counterclockwise pilot valves. This means that during theapplication of a clockwise pulse the chambers 67a and 67b of therespective clockwise pilot valves 38, 40 and 42 are in fluidcommunication.

When a clockwise pulse is applied to the clockwise pilot valves throughsignal conduit 120, a low (drain) pressure signal is communicated to thesignal port 96 of power valve 50 via segment 160a and signal conduit 160since chamber 67b of pilot valve 38 is in communication with drainpressure via sequencing conduit 158; a low (drain) pressure signal iscommunicated to the signal port of power valve 52 via segment 162a andsignal conduit 162 since chamber 67b of pilot valve' 40 is incommunication with drain pressure via sequencing conduit 154; and a high(supply) pressure signal is communicated to the signal port of powervalve 54 via segment 164a and signal conduit 164 since chamber 67b ofpilot valve 42 is in communication with supply pressure via sequencingconduit 156. The effects of such a pulse on the power valves are asfollows. The land 116 of power valve 50 remains in its illustratedposition and control port 102 continues to communicate with drainpressure via drain port 103; land 116 of power valve 52 moves upwardlyfrom its illustrated position into seating engagement with annularabutment 104, thereby effecting communication between control port 102and drain port 103; and land 116 of power valve 54 moves downwardly fromits illustrated position into seating engagement with annular abutment106, thereby effecting a communication between control port 102 andsupply pressure port 94. Therefore, such a pulse results in a lowpressure at the control ports of power valves 50 and 52 and a highpressure at the control port of power valve 54. The pulse produces nochanges in the pressures in the actuator chambers 22b, 25b, 28b and 31b(actuator group I), but simultaneously increases the pressures inactuator chambers 24b, 27b, 30b and 33b (actuator group III) anddecreases the pressures in actuator chambers 23b, 26b, 29b and 32b(actuator group II). Therefore, shafts 22s, 25s, 28s and 31:respectively move from ramps 14 to ramps 16 across surfaces 20, whileshafts 24s, 27s, 30s and 33s stroke into the rotor 10 along respectiveramps 16, thereby rotating the rotor in a clockwise manner. During thisrotation, as the chambers of the actuators of group II are incommunication with a low pressure, the ramps 14 respectively move shafts23s, 26s, 29s and 32s into the respective cylinders by virtue of theforces imparted thereto. After shafts 24s, 27s, 30s and 33s completetheir power strokes, the extremities thereof will abut the respectivelines 18, shafts 23s, 26s, 29s and 325 will abut the ramps 14 adjacentthe respective intersections of ramps 14 and surfaces 20, and shafts22s, 25s, 28s and 31s will abut ramps 16 adjacent the respectiveintersections of ramps 16 and surfaces 20.

In this new position, chambers 67b of respective pilot valves 38 and 46are in communication with the high (supply) pressure in chamber 24b viasequencing conduit 158, while the chambers 67b of the other pilot valvescommunicate with drain pressure. The stepping motor is now ready foranother signal pulse via either signal conduit 120 or 122.

It will be seen, therefore, that a succeeding clockwise signal pulsewill cause shafts 22s, 25s, 28s and 31s to undergo power strokes alongrespective ramps 16, thereby rotating the rotor 10 and forcing shafts24s, 27s, 30s and 33s away from the rotor towards their respectivecylinders. This pulse will, of course, produce no change in the finalpositions of shafts 23s, 26s, 29s and 32s.

A cursory examination of FIG. 3 will reveal that for counterclockwiserotation the master pistons stroke towards the rotor in the followingsequence: 22,24, 23, 22, 24, 23; and for clockwise rotation the masterpistons stroke in the following sequence: 24, 22, 23, 24, 22, 23, 24.

To recapitulate briefly, the master pistons and their respectiveassociated actuators form three actuator groups. The actuators of one ofthe groups stroke in unison inwardly to rotate the rotor, while theactuators of one of the other groups retract in unison under theinfluence of the force exerted upon them by the rotor. During the strokethe actuators of the remaining group remain essentially inactive. Forthe illustrated arrangement in FIGS. 1-3, each power stroke produces al5 rotor displacement. The actuator shafts of those actuators which areto initiate a power stroke are partially down their respective ramps,thereby ensuring that full output power will be available at thecommencement of actuation.

Sequencing is initiated when a power stroke is completed and a feedbacksignal (supply pressure behind the power piston) is fed to a clockwiseand a counterclockwise pilot valve. Then, either a clockwise orcounterclockwise signal is applied to the appropriate pilot valves whichresults in actuation of a power valve. Pressure communicated from thepower valve causes actuators of a group to undergo further powerstrokes. After the signal to the pilot valve terminates, the powervalve, which controls the power stroke, is locked in the open positionby a column of hydraulic fluid trapped between the power valve and pilotvalve. The trapped fluid, in effect, locks the rotor since the supplypressure keeps the shafts in firm contact with the respective lines 18.

The embodiment shown in FIGS. 4-6 includes a substantially identicalrotor and actuator group arrangement shown in FIGS. 1-3 except that thesequencing ports 22a, 23a and 24a are eliminated. The salientdifferences between the two embodiments are that the embodiment of FIG.4 makes use of permanent magnets in the rotor, which actuate adjacentswitches in the stator in order to furnish proper feedback sequencing,and utilizes solenoids to operate the power valves. In contradistinctionto the embodiment of FIG. 4, the embodiment of FIG. 3 makes use ofaseries of pilot valves and a conduit arrangement to accomplish the sameobjectives.

Referring now in detail to FIG. 4, the rotor 10 has a plurality ofpermanent magnets, designed by a sign, ounted around its peripheral edgein groups of two. Two juxtaposed magnets occupy an arc of 30. Theadjacent groups are spaced from one another by arcs equal to 15. Thespaces, designated 0,"between the neighboring groups are neutral.

Three power valves 200, 202 and 204 are adapted to deliver pressure tothe three groups of actuators I, II and III. Each power valve isoperated by a DC solenoid 206 having terminals T, and T The power valves200, 202 and 204 are represented in FIG. 4 by line diagrams usingstandard hydraulic symbols. As is hereinafter explained, the powervalves are hydraulically locked in position by respective pistons 207after actuation by the solenoids to lock the rotor againstdisplacements.

A supply pressure line 208 communicates with each of the power valves attheir respective pressure ports 210. Drain ports 212 are incommunication with sources of drain pressure (tank pressure) 214.Control ports 216 communicate with the chambers behind the actuatingpistons of the respective groups to communicate either supply or drainpressure thereto. Actuator locking port 213, which is blocked before thesolenoid is activated, is adapted to communicate with the drain port 212for reasons stated hereinafter. Each power valve is fluidly biasedupwardly to an inactive position,

wherein the chambers of the associated actuators are in communicationwith drain pressure.

The circuit which directs current through the solenoids comprisesterminals 218 and 220 which are adapted to be connected to a DC. (directcurrent) source of potential of any suitable design which is capable ofgenerating a DC. control signal pulse of sufficient power and durationto permit the power valves to function properly. The source must also becapable of reversing the polarity of the potential applied to theterminals to allow for rotor movement in either a clockwise orcounterclockwise direction. As indicated in FIG. 4, the polarity of theterminals 218 and 220 for clockwise and counterclockwise rotor movementis respectively minus-plus and plusminus.

Three magnetosensitive switches 222, 224 and 226 are fixedly positionedin the stator of the stepping motor at 30 intervals. The switches may beSPDT reed switches, magnetosensitive semiconductors, or other suitabletypes. The switches 222, 224 and 226 include repsective terminals (222a,222b), (224a, 2241;) and (226a, 226b). The switch terminals designatedby the suffix a" are connected to terminal 218 and the terminalsdesignated by the suffix b are connected to terminal 220.

As will be observed from FIG. 4 the terminals T, of the power valves200, 202 and 204 are connected to the switches 222, 224 and 266respectively, such that when a switch is closed, due to its beingpositioned adjacent a magnet in the rotor 10, terminal 218 is connectedto terminal T of the switchs associated power valve, and when a switchis open, due to its being positioned adjacent a neutral sector of therotor, terminal 220 is connected to the terminal T of the switchsassociated power valve. In the illustrated rotor position, switches 224and 226 are closed and switch 222 is open.

Junction terminals 230, 232 and 234, disposed between the switches andthe respective terminals T, of the power valves, are connected to therespective terminals T through uni laterally conducting diodes 236, 238and 240, which form an integral part of the logic circuit. Also, shuntdiodes 242, 244 and 246 are connected across the respective solenoids todissipate the energy stored in the field around the solenoid when thesignal pulse terminates.

Turning now to FIG. 5, wherein only the hydraulic circuit for lockingthe rotor and providing a bias torque is shown, the shafts 250 of thepistons 207 are respectively fixedly secured to the solenoid actuatedvalves for movement therewith. A hydraulic line 252 connected topressure line 22a serves to direct hydraulic fluid to and from cylinder254 of power valve 200 in which piston 207 is slideably mounted forforceably extending the piston against the hydraulic bias which opposesdownward piston movement. Hydraulic line 256, which communicates withlocking port 213 of power valve 200, embodies two check valves 256a and256b to allow only flow towards port 213 of power valve 200. Hydraulicline 256 is also connected to the pressure lines 23c and 24e andcylinders 254 of power valves 202 and 204. Hydraulic line 258, whichalso embodies two check valves 258a and 25812, is connected to pressureline 22e and communicates with locking port 213 of power valve 202intermediate the check valves thereof. Hydraulic line 258 is alsoconnected to hydraulic line 256 intermediate the latter lines connectionwith pressure line 24e and check valve 256 a. Hydraulic line 260, whichalso has two check valves 260a and 260b, connects with pressure line 232and communicates with locking port 213 of power valve 204. Hydraulicline 260 is connected at its end to hydraulic line 258 at a locationintermediate pressure line 22a and check valve 258a.

Shaft assemblies 262, disposed in the lower parts of the power valvesfunction like springs to respectively bias the valves to the positionsillustrated for power valves 200 and 204. The cylinders of these shaftassemblies respectively communicate with pressure supply line 208 bymeans of suitable conduits shown by dashed lines. Piston assemblies 207,in contrast to the shaft assemblies 262, only communicate with supplypressure when supply pressure is directed to their associated actuators.Piston assembly 207 is sized to exert a downward force larger than theupward force exerted by shaft.

assembly 262 so that the particular valve will remain positioned asshown in power valve 202 after the DC pulse terminates. Thus, ahydraulic lock is provided for the rotor assembly due to supply pressurebeing directed to the group of actuators whose shafts lie along therespective lines 18.

A preferred construction for the power valves 200, 202. and 204,symbolically illustrated in FIGS. 4 and 5, is shown in FIG. 6. Each ofthe power valves comprises a housing 264 having a cylindrical chamber265 therein in which a spool 266, with three spaced lands 268, 270 and272, is disposed for axial sliding movement. The spool is movablebetween an upper limit of travel, in which the outboard face of land 272is coincident with phantom line 274, and a lower limit of travel, inwhich the outboard face of land 268 is coincident with phantom line 276.An axial passageway 278 extends through spool 266 and communicates withfour transverse passages at each end of the spool to enable fluidtrapped at the ends of the chamber by lands 268 and 272 to be displacedduring upward and downward movements of the spool and thereby permituntrammeled sliding of the spool. The armature 206A of the solenoid 206is adapted to drive the spool downwardly when a signal is applied toterminals T and T by virtue of a shaft 282 which contacts the upper endof the spool. If the spool of valve 200 is in its lower position and apulse is applied to the terminals of either power valve 202 or 204, thespool of valve 200 is urged upwardly by shaft assembly 262 as cylinder254 is placed in communication with drain pressure as is hereinafterdescribed. It should be noted that the upward urging on spool 266 iscaused entirely by the supply pressure acting on the lower end of shaftassembly 262, the pressure being contained within chamber 284 by sea]286. The reason for not employing a spring to provide upward bias isthat a spring would move the spool from the lower limit position to theupper limit position if supply pressure were to decrease and this wouldnot permit a subsequently increased supply pressure to be directed tothe associated actuators. in the instant arrange ment, should supplypressure be lost during stroking of a group of actuators, when pressurereturns these actuators will continue their previously interruptedstrokes. Also, this feature assures restoration of the hydraulic rotorlock upon resumption of the supply pressure, should the rotor be in alocked position when supply pressure decreases.

For purposes of describing the manner of operation of the latterembodiment, assume that a voltage is applied to the terminals 218 and220 in order to initate a counterclockwise step movement of the rotor10. The applied voltage results in a potential difference betweenjunction terminals 232 and 234 which induces a current in the solenoidof power valve 204, thereby driving the spool 266 thereof downwardly.Although a potential difference exists between junction terminals 230and 234, the diode 236 prevents any significant current from flowingthrough the solenoid of power valve 200. No current will flow throughthe solenoid of power valve 202 since junction terminals 230 and 232 arereferenced to the same potential. The result produced by this pulse isconsequently a downward displacement of the spool of power valve 204.

The resulting effect of this downward displacement is communicationbetween port 210 and port 216 and communication between port 213 andport 212 (note that the symbolical port 212 of FIG. 4 is in reality twoports as shown in FIG. 6, both of which communicate with tank 214).Hence, supply pressure is simultaneously directed to the actuators ofgroup III and the piston assembly 207 of power valve 204. The pressuredirected to the piston assembly of the power valve 204 holds the spoolthereof in its lower limit of travel to maintain communication betweenports 213 and 212 and between ports 210 and 216 of power valve 204untilanother pulse is applied to terminals 218 and 2207 Also, when thespool of power valve 204 is in its lower limit of travel, the actuatorsof group I] and the piston assembly 207 of power valve 202 communicatewith tank pressure via hydraulic line 260, check valve 260b, and port213. This allows the shaft assembly of power valve 202 to move the spoolto its upper limit of travel. When the spool of power valve 202 reachesits upper limit of travel, the actuators of group ll are connectedthrough port 216 to tank 214 and pressure is generated in pressure line24c to actuator group III.

The hydraulic circuit of FIG. precludes supply pressure from beingapplied to any actuator group until the actuator group, which is incurrent communication with supply pressure, is vented. When the spool ofpower valve 204 reaches its lower limit of travel, supply pressure fromthe port 210 thereof will be vented to the tank 214 of power valve 202via hydraulic line 256, check valve 258b, port 213 of power valve 202and port 212 of power valve 202. When the pressure in line 23edissipates to such an extent that shaft assembly 262 of power valve 202overcomes the force exerted by the opposing piston and moves the spoolof power valve 202 upwardly, pressure will be applied to the actuatorsof group Ill. The circuit of FIG. 5 then renders it impossible topressurize a group of actuators until the spool of the power valveassociated with the pressurized actuators is displaced upwardly.

This applied pulse, of course, has no affect on power valve 200 exceptfor the fact that the piston assembly 207 and actuator group 1 thereofare placed in communication with tank pressure via hydraulic line 258,hydraulic line 260, check valve 260a and port 213 of power valve 204,whereas, prior to the pulse, it will be noted that the actuators ofgroup I and the piston assembly of power valve 200 were in communicationwith tank pressure via hydraulic line 258, check valve 258a, and port213 of power valve 202. Before and after the pulse the actuators ofgroup I and the piston assembly of power valve 200 also communicate withtank pressure via port 216 of power valve 200.

Therefore, the applied pulse causes the actuators of group III tostroke, thereby rotating the rotor in a counterclockwise directionthrough a step,

After the rotation of rotor 10 is completed, a feedback signal isdirected to the logic circuit via switches 222 and 226 which are nowrespectively connected to terminals 218 and 220, the switch 224remaining connected to terminal 218 since it is adjacent another magneton rotor 10. When the next counterclockwise pulse is applied toterminals 218 and 220 the solenoid of power valve 202 will be activated.It will be seen that the sequence of actuation of the power valves ofFIG. 4 for counterclockwise rotation is: 204, 202, 200, 204, 202, 200;while for clockwise rotation the sequence is: 200, 202, 204,200,202,204,200.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practices otherwise than as specifically described.

What We Claim ls:

1. A fluid operated stepping motor comprising:

a source of supply pressure;

a source of drain pressure;

an output member, having a cyclic edge profile,

bidirectionally movable between a plurality of discrete positions;

three fluid operated actuators arranged adjacent the output member foradvancing the output member by successive engagement with the profilethereof, each actuator having a fully extended position and a retractedposition, a selected actuator being in the fully extended position andthe other actuators being in retracted positions in the discretepositions of the output member;

power valve means to connect the actuators to the sources of supplypressure and drain pressure;

logic means adapted to receive bi-directional, digital, command signalpulses to control the power valve means such that supply pressure isdirected to the selected actuator while drain pressure is directed tothe other actuators and such that supply pressure is continuouslydirected to the selected actuator after termination of the signal pulseto drive the output member to a discrete position and provide a positiveposition lock thereafter;

means to communicate the signal pulses to the logic means;

and

a discrete feedback control operatively connected to the logic means forgenerating a feedback signal thereto as the output member assumes adiscrete position such that an actuator different from the previouslyselected actuator is advanced from the retracted position to theextended position by a succeeding signal pulse to drive the outputmember to an adjacent discrete position.

2. A fluid operated stepping motor, as defined in claim 1.

wherein the feedback control comprises:

a plurality of permanent magnets mounted on the output member; and

a plurality of magnetosensitive switches positioned adjacent the outputmember and actuable thereby.

3. A fluid operated stepping motor, as defined in claim 1,

wherein said feedback control comprises:

a plurality of sequencing conduits connected to the actuators forgenerating fluid feedback signals to the logic circuit.

4. A fluid operated stepping motor, as defined in claim 1, wherein theoutput member comprises an output shaft carrying a rotor.

5. A fluid operated stepping motor, as defined in claim 1, furtherincluding:

bias means, operable upon an increase in supply pressure after adepletion thereof, to drive the output member from a positionintermediate two adjacent discrete positions to a discrete position sothat proper sequencing of the actuators may be affected by a subsequentsignal pulse.

6. A fluid operated stepping motor comprising:

a source of supply pressure;

a source of drain pressure;

a rotor, having a cyclic edge profile, bi-directionally movable betweena plurality of discrete positions;

three groups of fluid operated actuators arranged adjacent the outputmember for successively advancing the output member by engagement withthe profile thereof, each group comprising a plurality of actuatorspositionable in unison between corresponding positions, each actuatorhaving a fully extended position and a retracted position, the actuatorsof a selected group being in extended positions and the actuators of theother groups being in retracted positions in the discrete positions ofthe rotor,

power valve means to connect the groups to the sources of supplypressure and drain pressure;

logic means adapted to receive bi-directional, digital, command signalpulses to control the power valve means such that supply pressure isdirected to the selected group while drain pressure is directed to theother groups and such that supply pressure is continuously directed tothe selected group after termination of the signal pulse to drive therotor to a discrete position and provide a positive position lockthereafter;

means to communicate the signal pulses to the logic means;

and

a discrete feedback control operatively connected to the logic means forgenerating a feedback signal thereto as the rotor assumes a discreteposition such that the actuators of a group different from thepreviously selected group are advanced from the retracted positions tothe extended positions by a succeeding signal pulse to drive the rotorto an adjacent discrete position.

7. A fluid operated stepping motor, as defined in claim 6,

wherein the feedback control comprises:

a plurality of permanent magnets mounted on the output member; and

a plurality of magnetosensitive switches positioned adjacent the outputmember and actuable thereby.

8. A fluid operated stepping motor, as defined in claim 6, wherein thefeedback control comprises:

a plurality of sequencing conduits connected to the actuators forgenerating fluid feedback signals to the logic circuit.

9. A fluid operated stepping motor, as defined in claim 6, wherein bothsides of the rotor have a cyclic edge profile and wherein half of theactuators are arranged on one side of the rotor and half of theactuators are arranged on the other side of the rotor such that eachactuator is parallel to the shaft and in axial alignment with anotheractuator of the same group.

10. A fluid operated stepping motor comprising:

a rotor having a plurality of pairs of converging ramps formed on atleast one side thereof;

a plurality of actuators positioned adjacent the rotor parallel to theaxis of the rotor for selectively engaging the ramps to rotate therotor;

a logic circuit operatively connected to the actuators for selectivelydirecting pressurized fluid thereto;

a discrete feedback control operatively connected to the logic circuitfor generating a feedback signal thereto representative of a discreteposition of the rotor; and the feedback control comprising:

a plurality of permanent magnets mounted on the rotor; and

a plurality of magnetosensitive switches positioned adjacent the rotorand actuable thereby.

11. A fluid operated stepping motor comprising:

a rotor having a plurality of pairs of converging ramps formed on atleast one side thereof;

a plurality of actuators positioned adjacent the rotor parallel to theaxis of the rotor;

a logic circuit operatively connected to the actuators for selectivelydirecting pressurized fluid thereto;

a discrete feedback control operatively connected to the logic circuitfor generating a feedback signal thereto representative of a discreteposition of the rotor; and the feedback control comprising:

a plurality of sequencing conduits connected to the actuators forgenerating fluid feedback signals.

1. A fluid operated stepping motor comprising: a source of supplypressure; a source of drain pressure; an output member, having a cyclicedge profile, bidirectionally movable between a plurality of discretepositions; three fluid operated actuators arranged adjacent the outputmember for advancing the output member by successive engagement with theprofile thereof, each actuator having a fully extended position and aretracted position, a selected actuator being in the fully extendedposition and the other actuators being in retracted positions in thediscrete positions of the output member; power valve means to connectthe actuators to the sources of supply pressure and drain pressure;logic means adapted to receive bi-directional, digital, command signalpulses to contRol the power valve means such that supply pressure isdirected to the selected actuator while drain pressure is directed tothe other actuators and such that supply pressure is continuouslydirected to the selected actuator after termination of the signal pulseto drive the output member to a discrete position and provide a positiveposition lock thereafter; means to communicate the signal pulses to thelogic means; and a discrete feedback control operatively connected tothe logic means for generating a feedback signal thereto as the outputmember assumes a discrete position such that an actuator different fromthe previously selected actuator is advanced from the retracted positionto the extended position by a succeeding signal pulse to drive theoutput member to an adjacent discrete position.
 2. A fluid operatedstepping motor, as defined in claim 1, wherein the feedback controlcomprises: a plurality of permanent magnets mounted on the outputmember; and a plurality of magnetosensitive switches positioned adjacentthe output member and actuable thereby.
 3. A fluid operated steppingmotor, as defined in claim 1, wherein said feedback control comprises: aplurality of sequencing conduits connected to the actuators forgenerating fluid feedback signals to the logic circuit.
 4. A fluidoperated stepping motor, as defined in claim 1, wherein the outputmember comprises an output shaft carrying a rotor.
 5. A fluid operatedstepping motor, as defined in claim 1, further including: bias means,operable upon an increase in supply pressure after a depletion thereof,to drive the output member from a position intermediate two adjacentdiscrete positions to a discrete position so that proper sequencing ofthe actuators may be affected by a subsequent signal pulse.
 6. A fluidoperated stepping motor comprising: a source of supply pressure; asource of drain pressure; a rotor, having a cyclic edge profile,bi-directionally movable between a plurality of discrete positions;three groups of fluid operated actuators arranged adjacent the outputmember for successively advancing the output member by engagement withthe profile thereof, each group comprising a plurality of actuatorspositionable in unison between corresponding positions, each actuatorhaving a fully extended position and a retracted position, the actuatorsof a selected group being in extended positions and the actuators of theother groups being in retracted positions in the discrete positions ofthe rotor; power valve means to connect the groups to the sources ofsupply pressure and drain pressure; logic means adapted to receivebi-directional, digital, command signal pulses to control the powervalve means such that supply pressure is directed to the selected groupwhile drain pressure is directed to the other groups and such thatsupply pressure is continuously directed to the selected group aftertermination of the signal pulse to drive the rotor to a discreteposition and provide a positive position lock thereafter; means tocommunicate the signal pulses to the logic means; and a discretefeedback control operatively connected to the logic means for generatinga feedback signal thereto as the rotor assumes a discrete position suchthat the actuators of a group different from the previously selectedgroup are advanced from the retracted positions to the extendedpositions by a succeeding signal pulse to drive the rotor to an adjacentdiscrete position.
 7. A fluid operated stepping motor, as defined inclaim 6, wherein the feedback control comprises: a plurality ofpermanent magnets mounted on the output member; and a plurality ofmagnetosensitive switches positioned adjacent the output member andactuable thereby.
 8. A fluid operated stepping motor, as defined inclaim 6, wherein the feedback control comprises: a plurality ofsequencing conduits connected to the actuators for generating fluidfeedback signals to the loGic circuit.
 9. A fluid operated steppingmotor, as defined in claim 6, wherein both sides of the rotor have acyclic edge profile and wherein half of the actuators are arranged onone side of the rotor and half of the actuators are arranged on theother side of the rotor such that each actuator is parallel to the shaftand in axial alignment with another actuator of the same group.
 10. Afluid operated stepping motor comprising: a rotor having a plurality ofpairs of converging ramps formed on at least one side thereof; aplurality of actuators positioned adjacent the rotor parallel to theaxis of the rotor for selectively engaging the ramps to rotate therotor; a logic circuit operatively connected to the actuators forselectively directing pressurized fluid thereto; a discrete feedbackcontrol operatively connected to the logic circuit for generating afeedback signal thereto representative of a discrete position of therotor; and the feedback control comprising: a plurality of permanentmagnets mounted on the rotor; and a plurality of magnetosensitiveswitches positioned adjacent the rotor and actuable thereby.
 11. A fluidoperated stepping motor comprising: a rotor having a plurality of pairsof converging ramps formed on at least one side thereof; a plurality ofactuators positioned adjacent the rotor parallel to the axis of therotor; a logic circuit operatively connected to the actuators forselectively directing pressurized fluid thereto; a discrete feedbackcontrol operatively connected to the logic circuit for generating afeedback signal thereto representative of a discrete position of therotor; and the feedback control comprising: a plurality of sequencingconduits connected to the actuators for generating fluid feedbacksignals.